1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to data error interpolation processing.
2. Related Background Art
Wavelet transform processing using a subband encoding technique has conventionally been known. FIG. 7 is a block diagram showing a conventional encoder which performs two-dimensional wavelet transform. FIG. 8 is a block diagram showing a conventional decoder which decodes two-dimensionally wavelet-transformed data. FIG. 6 is a schematic view showing the space before and after the two-dimensional wavelet transform.
Two-dimensional wavelet transform performs high- and low-pass filter processes in the horizontal and vertical directions on input image data, and transforms the data into a plurality of subband components formed from data corresponding to different spatial frequency bands. For example, subband-transformed image data 602 is obtained as a result of performing wavelet transform processing on an image 601 in FIG. 6.
Data having undergone horizontal high-pass filter processing and then vertical high-pass filter processing is transformed into data corresponding to the HH area of the data 602. Data having undergone horizontal high-pass filter processing and then vertical low-pass filter processing is transformed into data corresponding to the HL area of the data 602. Data having undergone horizontal low-pass filter processing and then vertical high-pass filter processing is transformed into data corresponding to the LH area of the data 602. Data having undergone horizontal low-pass filter processing and then vertical low-pass filter processing is transformed into data corresponding to the LL area of the data 602.
For descriptive convenience, wavelet transform of level 1 has been explained. It is also possible to perform wavelet transform of level 2 which executes high- and low-pass filter processes in the horizontal and vertical directions on data of the LL area of the data 602 and transforms the data into a subband, or wavelet transform of level 3 which executes high- and low-pass filter processes in the horizontal and vertical directions on data of the LL area having undergone wavelet transform of level 2 and transforms the data into a subband.
In practice, wavelet transform is performed to a feasible level, thus implementing hardware. A two-stage processing method using a primary filter as shown in FIG. 7 is generally adopted when two-dimensional wavelet transform is to be done as hardware.
In FIG. 7, image data input from an input unit 701 is output to two horizontal filters. One horizontal filter is a horizontal low-pass filter 702, and the other is a horizontal high-pass filter 703. Data processed by the horizontal LPF 702 and horizontal HPF 703 are respectively output to down-samplers 704 and 705. The down-samplers 704 and 705 thin out input image data every other sample to halve the data amount.
The respective data having undergone the two types of horizontal filter processes is then subjected to vertical filter processing.
This filter processing is done by four filters: a vertical LPF 706 for data having passed through the horizontal LPF 702, a vertical HPF 707 for data having passed through the horizontal LPF 702, a vertical LPF 708 for data having passed through the horizontal HPF 703, and a vertical HPF 709 for data having passed through the horizontal HPF 703. Data processed by the vertical filters are thinned out to ½ the data amount by down-samplers 710, 711, 712, and 713.
In this manner, input image data is divided into four subband components, i.e., LL, LH, HL, and HH data. The four subband components are output from LL, LH, HL, and HH output units 714, 715, 716, and 717. The output data are transmitted through a radio communication channel, wire communication path, or recording medium.
FIG. 8 is a block diagram showing a decoder which decodes, into original image data, data which has undergone two-dimensional wavelet transform processing and is transmitted through a transmission path.
Subband component data input to LL, LH, HL, and HH input units 801, 802, 803, and 804 are output to vertical up-samplers 805, 806, 807, and 808. The up-samplers 805 to 808 insert zero data between two samples of input data to double the number of samples.
After up-sampling processing, LL, LH, HL, and HH components are respectively output to a synthesization vertical LPF 809, synthesization vertical HPF 810, synthesization vertical LPF 811, and synthesization vertical HPF 812. The synthesization vertical LPF 809, synthesization vertical HPF 810, synthesization vertical LPF 811, and synthesization vertical HPF 812 filter the input data, and synthesize samples corresponding to zero data inserted by the up-samplers 805 to 808. Outputs from the synthesization vertical LPF 809 and synthesization vertical HPF 810 are output to an adder 813, whereas outputs from the synthesization vertical LPF 811 and synthesization vertical HPF 812 are output to an adder 814. The adders 813 and 814 add data from these filters to synthesize the vertical components.
Outputs from the adders 813 and 814 are output to horizontal up-samplers 815 and 816. The up-samplers 815 and 816 insert zero data between two samples to double the number of samples. LL and LH components are output to a synthesization horizontal LPF 817, and HL and HH components are output to a synthesization horizontal HPF 818. The synthesization horizontal LPF 817 and synthesization horizontal HPF 818 filter the input data, and synthesize samples corresponding to zero data inserted by the up-samplers 815 and 816. Outputs from the synthesization horizontal LPF 817 and synthesization horizontal HPF 818 are added by an adder 819 to synthesize the horizontal components. The data is decoded into original image data, which is output from an output unit 820.